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<table width="100%" summary="page for rhDNase"><tr><td>rhDNase</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>rhDNASE data set</h2>

<h3>Description</h3>

<p>Results of a randomized trial of rhDNase for the treatment of cystic
fibrosis.
</p>


<h3>Format</h3>

<p>A data frame with 767 observations on the following 8 variables.
</p>

<dl>
<dt><code>id</code></dt><dd><p>subject id</p>
</dd>
<dt><code>inst</code></dt><dd><p>enrolling institution</p>
</dd>
<dt><code>trt</code></dt><dd><p>treatment arm: 0=placebo, 1= rhDNase</p>
</dd>
<dt><code>entry.dt</code></dt><dd><p>date of entry into the study</p>
</dd>
<dt><code>end.dt</code></dt><dd><p>date of last follow-up</p>
</dd>
<dt><code>fev</code></dt><dd><p>forced expriatory volume at enrollment, a measure
of lung capacity</p>
</dd>
<dt><code>ivstart</code></dt><dd><p>days from enrollment to the start of IV antibiotics</p>
</dd>
<dt><code>ivstop</code></dt><dd><p>days from enrollment to the cessation of
IV antibiotics</p>
</dd>
</dl>



<h3>Details</h3>

<p>In patients with cystic fibrosis, extracellular DNA is released by
leukocytes that accumulate in the airways in response to chronic bacterial
infection.
This excess DNA thickens the mucus, which then cannot be cleared from the
lung by the cilia.  The accumulation leads to exacerbations of
respiratory symptoms and progressive deterioration of lung function.
At the time of this study 
more than 90% of cystic fibrosis patients eventually died of lung
disease.
</p>
<p>Deoxyribonuclease I (DNase I) is a
human enzyme normally present in the mucus of human lungs that digests
extracellular DNA.
Genentech, Inc. cloned a highly purified recombinant DNase I (rhDNase or
Pulmozyme) which when delivered to the lungs in an aerosolized form cuts
extracellular DNA, reducing the viscoelasticity of airway
secretions and improving clearance.
In 1992 the company
conducted a randomized double-blind trial comparing rhDNase to placebo.
Patients were then monitored for
pulmonary exacerbations, along with measures of lung volume and flow.
The primary endpoint was the time until
first pulmonary exacerbation; however, data on all exacerbations were
collected for 169 days.
</p>
<p>The definition of an exacerbation was an infection that required the use
of intravenous (IV) antibiotics.  Subjects had 0&ndash;5 such episodes during
the trial, those with more than one have multiple rows in the data
set, those with none have NA for the IV start and end times.
A few subjects were infected at the time of enrollment, subject 173 for
instance has a first infection interval of -21 to 7.  We do not count this
first infection as an &quot;event&quot;, and the subject first enters the risk set
at day 7.
Subjects who have an event are not considered to be at risk for another
event during the course of antibiotics, nor for an additional 6 days
after they end.  (If the symptoms reappear immediately after cessation
then from a medical standpoint this would not be a new infection.)
</p>
<p>This data set reproduces the data in Therneau and Grambsch, is does not
exactly reproduce those in Therneau and Hamilton due to data set updates.
</p>


<h3>References</h3>

<p>T. M. Therneau and P. M. Grambsch, Modeling Survival Data: Extending
the Cox Model, Springer, 2000.
</p>
<p>T. M. Therneau and S.A. Mamilton,
rhDNase as an example of recurrent event analysis, Statistics
in Medicine, 16:2029-2047, 1997.
</p>


<h3>Examples</h3>

<pre>
# Build the start-stop data set for analysis, and
#  replicate line 2 of table 8.13
first &lt;- subset(rhDNase, !duplicated(id)) #first row for each subject
dnase &lt;- tmerge(first, first, id=id, tstop=as.numeric(end.dt -entry.dt))

# Subjects whose fu ended during the 6 day window are the reason for
#  this next line
temp.end &lt;- with(rhDNase, pmin(ivstop+6, end.dt-entry.dt))
dnase &lt;- tmerge(dnase, rhDNase, id=id,
                       infect=event(ivstart),
                       end=  event(temp.end))
# toss out the non-at-risk intervals, and extra variables
#  3 subjects had an event on their last day of fu, infect=1 and end=1
dnase &lt;- subset(dnase, (infect==1 | end==0), c(id:trt, fev:infect))
agfit &lt;- coxph(Surv(tstart, tstop, infect) ~ trt + fev, cluster=id,
                 data=dnase)
</pre>


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